Microscopic studies of gingival biopsies from humans with advanced adult periodontal disease have shown the presence of oral spirochetes within the periodontal tissues (Frank 1980, Saglie 1982, Wolinsky 1985). It has been suggested that these and other periodontal pathogens originate from within the periodontal pocket and their movement through the gingival crevicular epithelium represents a key event in the progression of destructive periodontal disease. Presently, little information is known about the cellular events leading up to bacterial penetration. It is the specific aim of this investigation to test the hypothesis that oral treponemes infiltrate the gingival tissues through the initial attachment to the gingival sulcular epithelium followed by alteration in the epithelial cell layer eventually leading to the movement of the treponemes through the intercellular epithelial junctions. To test this hypothesis, the attachment, penetration, and movement of radiolabeled treponema sp. through primary cultures of human gingival epithelial cells will be studied. The hypothesis predicts that oral treponemes are able to infiltrate the underlying gingival connective tissues in a highly specific fashion. The resultant weakening of the epithelium structure following treponemal interaction may promote the active or passive ingression of other periodontal pathogenic bacteria. Infiltration of the epithelium by oral Treponemes may be one of many signals which hallmark the onset of active periodontal disease. The results of this study will be used to develop a useful in vitro tissue culture system for studying bacterial interaction with host tissues. The data from this investigation will form the foundation for a larger study. We believe the results of this study will help expand our understanding of the progression of periodontal disease.